Take the lint error out of main (#6)

`npm run lint` fails on main, and has since CI was added, so every pull
request opened against it starts red for a reason that has nothing to do
with the change in it. Two unrelated PRs came back with the same failure,
which is how it was found.

    vite.config.ts
      1:1  error  Do not use a triple slash reference for vitest/config,
                  use `import` style instead

The reference was doing one job: putting the `test` key in scope for
defineConfig. Importing defineConfig from vitest/config rather than vite
does the same job in the style the rule asks for, and the file already
imported configDefaults from there on the next line.

vite.config.ts

@@ -1,6 +1,7 @@
-/// <reference types="vitest/config" />
+// defineConfig comes from vitest/config rather than vite, which is what puts
-import { configDefaults } from 'vitest/config'
+// the `test` key below in scope. It replaces a triple-slash reference that did
-import { defineConfig } from 'vite'
+// the same job and that eslint rejects.
+import { configDefaults, defineConfig } from 'vitest/config'
 import react from '@vitejs/plugin-react'
 import tailwindcss from '@tailwindcss/vite'
 import path from 'path'